16 HICKSj ON GONIDIA OF LICHEXS. 



his^ and also point out that it arises from v/itliin. the sori- 

 dhon, and that, under varied circumstances, the changes 

 Avhich the lichen-gonidium undergoes are far more diversi- 

 fied than has been hitherto suspected. 



If we observe carefully the gonidia on Cladonia pyxidatu, 

 we find them, generally at least, passing through the seg- 

 mental stage in the same way as those of Parmelia, for 

 instance, and in the same way as in Chlorococcus ;* and to 

 proceed, in coiu'se of time, to the formation of soridia, by 

 similar stages ; and this holds if this lichen be growing in a 

 dry position, or during a hot or dry season ; but should the 

 weather become damp, or the plant grow in a moist situa- 

 tion, or be removed to one, then the changes which form 

 the basis of this fasciculus appear very constantly. I have 

 noticed it in specimens from so many parts of the south of 

 England, that it may, Avithout hesitation, be said to be a 

 normal condition. 



To observe the early changes it will be necessary to break 

 up the soridium by pressure, or otherwise ; after a time 

 the contents escape from one side of the soridium, or break 

 up the whole simultaneously. 



The first change observable is, that some of the segments be- 

 come enveloped by a layer of mucus, inside of which subdivi- 

 sion still further proceeds, the portions in most cases possess- 

 ing, after a little time, each a separate mucous envelope. This 

 is shown in Plate II, at figs. 4, 6, 7. Thus, we have all the 

 elements of a Gleocapsa (Kiitzing) growth. At first, com- 

 monly, the subdivision is maintained on the binary plan, 

 which may continue for some time, as at fig. 7. Frequently 

 the quaternary plan prevails, as at fig. 10. After a while the 

 subdivisions become separated, each with a mucous layer, as 

 in the smaller cells at fig. 8, the process of segmentation 

 being arrested. Again, in some the mucous envelope of 

 the original cell does not dissolve away while segmentation 

 proceeds Avithin, so that many of the Gleocapsiform cells 

 have from one to three common em'clopes (fig. 11, a, a, fig. 

 14, a, a, Szc. &c). A condition being thus produced similar 

 to Hassall's H(Bmatococcus riipestris {Gleocapsa pohjdermatica , 

 Kiitzing) . In the same mass — the produce of the Cladonia- 

 soridia — will be found every variety of subdivision, each 

 form constituting a mass of a greater or smaller extent; 

 generally, I may observe, (and this is a point Avorthy of 

 notice,) but not always indiscriminately mingled, as if a 

 particular kind haAang once commenced, it would, circura- 



* Sec Easciculus I, ' Microscopical Journal/ Oct., 1860. 



